Conventionally, a propelling machine of a vessel comprises an internal combustion engine, a power transmission device, and others. The power transmission device decelerates driving force of the engine, and drives a propeller connected to the power transmission device. When the vessel is propelled, the engine is always driven. Even if the vessel sails at low speed, the propeller is driven by the engine. Consequently, exhaust gas, vibration and noise always occur while propelling.
Moreover, inboard electrical equipments are supplied with electric power stored in a battery. A generator for charging electric power to the battery is attached to the internal combustion engine of the propelling machine.
Unless the vessel sails at maximum speed, the internal combustion engine driving the propeller reserves power at any rotational speed because its maximum output force is larger than load on the vessel.
In view of the above, the present invention is directed to establish an arrangement of an electric motor in a propelling machine, wherein reserved power of an internal combustion engine is converted into electric power for driving the electric motor so that a propeller can be driven by only the electric motor or by the engine with assist of the electric motor.
In the above aspect, the present invention is also directed to establish a mechanism for preventing excessive torque and protecting shafts when output power of the electric motor is transmitted to the propelling system, and to establish a cooling manner for stabilizing output power of the electric motor.